dialectric grease and zincs

[blueazimuth]

I have a production aluminium boat, and there is a neoprene pad between zinc and hull, and Sitex is filled into bolt hole, to keep bolts dry, and not in contact with water.
It sounds complicated, but it's not, and for the French VIA Marine aluminium boats, it is the correct way to install the zincs. It's interesting to note that a very experienced surveyor, in Trinidad, having never seen this type of insulation, told me "get it off - it's all wrong, and your insurance won't be valid until you do". And wrote his survey up that way. He is flat wrong: every VIA I have seen, and I've seen 7, all have the neoprene pad / Sitex installation. I took photos, sent them to the insurance company and their sources verified that the installation was correct.
Having said that, dielectric grease should not be used - dielectric grease insulates, and zincs need to be in electrical contact.

[Paul Elliott]

Originally Posted by chris95040

I won't argue against the folks saying the grease will squeeze out and contact will still be made, but in that case what is the logic in favoring dielectric (electrically insulating) grease on a connection that's supposed to conduct?

Because you like that it contains the word 'electric' ?

It's because the grease helps prevent oxidation corrosion. This corrosion can push otherwise conducting surfaces apart, and the corrosion is not a good conductor. In high-current applications this high-resistance corrosion can become quite hot and of course cause voltage drops.

As has been said, mating metal surfaces will make contact through the grease, at the same points where they would make contact without the grease. The grease flows away from the actual points of contact, and prevents oxidation near those points of contact.

As for using dielectric or other grease on zincs, I can't see that it does any harm, and it might help. I've not used it there and have had no problems, other than the zincs sacrificing themselves as they are supposed to do. Grease wouldn't, and shouldn't, stop that.

[senormechanico]

If anybody's interested, you don't need to wonder if there's continuity or not.
Just take any two hunks of metal, bolt them together through some insulating material such as wood or plastic. Using an ohmmeter, measure the resistance. Basically zero.

Disassemble, then after applying a dielectric grease to the bolt, reassemble again and use an ohmmeter across them.

Any difference?

[Paul L]

Originally Posted by Paul Elliott

It's because the grease helps prevent oxidation corrosion. This corrosion can push otherwise conducting surfaces apart, and the corrosion is not a good conductor. In high-current applications this high-resistance corrosion can become quite hot and of course cause voltage drops.

As has been said, mating metal surfaces will make contact through the grease, at the same points where they would make contact without the grease. The grease flows away from the actual points of contact, and prevents oxidation near those points of contact.

As for using dielectric or other grease on zincs, I can't see that it does any harm, and it might help. I've not used it there and have had no problems, other than the zincs sacrificing themselves as they are supposed to do. Grease wouldn't, and shouldn't, stop that.

A solution looking for a problem. Maintaining a boat is complicated enough - why complicate an easy maintanance item like changing zincs?

[wsmurdoch]

One place that I have learned NOT to use grease in assembling a zinc is with a prop nut anode. I used to grease the socket head cap screw threads. It was a mistake just like greasing the wheel nuts on a car or trailer. They unscrew. It took me losing a few before I realized what I was doing wrong. I now use Blue Loctite on the screw -- the waxy kind that comes in a Chapstick-like stick. I have not lost one since.

https://www.amazon.com/Loctite-Quick.../dp/B000132VH6
Propeller Nuts Complete With Zinc Anode

[jamhass]

Never use grease on a zinc. Protection REQUIRES a good electrical connection between the zinc and whatever it is protecting. Most greases, and especially dielectric greases are insulators. A tiny bit to lube the screws is OK, just don't overdo it.